Build Non-Conforming Single Family? Too Risky?

[Nicole S.]

I currently own a single family rental in a single family zone right in the heart of the city of Seattle. The home is old, built in 1919 with original plumbing, wiring and two major floor to ceiling cracks in the foundation. The lot is 6,250 SF and the home is 2,320 SF.  I own it free and clear and I make a pathetic $1,200/month (compared to what I could get if the home weren't in such bad shape). 

The home is not worth rehabbing, I plan to demolish and re-construct. I plan to re-construct another three story, single family home with an attached ADU. I would place one tenant in the top two floors, one in the basement and one in the ADU.

MY QUESTION: the city would probably view this as a triplex which the land is not zoned for. I have been researching and planning this tear down for near a decade and just hired the architect. He tells me re-zoning in Seattle is a nightmare and now with the new rental registration ordinance, the city can inspect and if they do, my non-conforming triplex could  be discovered. Of course for the build the city would get one set of plans and we would operate from another set of plans, not finishing the two additional "units" until after a certificate of occupancy and inspection has been performed. 

Reading posts on here about folks buying non-conforming property suggest that there are appraisal, resale and insurance consequences involved. 

Have I answered my own question here? Do I risk this and build it anyway? It will look like a typical single family from the exterior. Or, do I build a regular single family home and rent it to ONE renter? Seems like such a waste of space and land.